Site ventilation of a long deep tunnel: The lot Bodio of the Gotthard base tunnel

In the future several very long tunnels with a high overburden are going to be built in Europe and all around the world. These structures mostly consist of two parallel running tunnels plus cross passages at regular distances. Generally all of these constructions are divided into several lots and consist of a combination of TBM or shield drives together with NATM drives. The automated drives tend to achieve 10,000 meters in length and beyond, cross passages or other special cross sections are usually carried out by NATM. Thus they comprise a huge challenge regarding the supply of fresh air. Fumes of the drill-and-blast-sections, exhaust gases, any dust created through excavating or mucking, etc. have to be extracted and fresh air has to be brought up to the TBMs heads. Due to the extreme lengths and the need to simultaneously casting the inner lining the application of flexible ventilation ducts to carry the fresh air from the exterior to the tunnel head is almost impossible. Therefore a recirculation ventilation system is established during construction.